By kind of work
Planting a forest and handing out saplings in a parking lot are both tree planting. They are not the same job. An organization can do several.
ReforestationReplanting trees on land that was recently forested, restoring degraded or cleared forests.38 organizationsAfforestationEstablishing new forests on land that was not previously forested.6 organizationsUrban forestryPlanting and caring for trees in cities, neighborhoods, streets, parks and schoolyards.24 organizationsTree adoption & giveawaysDistributing free or low-cost trees to residents to plant at home, often at live events.13 organizationsAgroforestryIntegrating trees with crops and livestock to improve farmer livelihoods and soil.19 organizationsMangrove restorationRestoring coastal mangrove forests for carbon storage, fisheries and storm protection.5 organizationsNurseries & seedlingsGrowing seedlings and saplings for planting programs.19 organizationsSeed collectionCollecting, banking and distributing native tree seed.8 organizationsTree care & maintenanceWatering, pruning, mulching and long-term stewardship of planted trees.9 organizationsEducation & advocacyTraining, community education, policy work and public campaigns for trees.33 organizationsCarbon offset plantingPlanting funded by or generating carbon credits and corporate offsets.10 organizationsFood forests & orchardsPlanting fruit and nut trees for community food security.8 organizationsDisaster & fire recoveryReplanting after wildfire, storms, floods or other disasters.6 organizationsResearch & monitoringMeasuring survival, growth and ecological outcomes of planting efforts.10 organizations